shimano road bike wheels why do they have a max capacity of 30t

As in the title I've just unpacked some r501 wheels and on the instructions it says a max cacity of 30t. I've tried a 32t cassette on it and it doesn't appear to be causing a problem , so just wondering why they would state that

because thats the biggest cassette they sell for road bikes. When the biggest road cassette they sold was 27/28 their rear mechs were only rated to 27/28, as soon as they introduced a bigger cassette the limits changed, and I assume they did the same with their wheels. Shimano have always had a rep for being conservative with limits, if you google it theres forum threads/posts for years with people discussing running bigger cassettes than rear mechs were rated for with no problems whatsoever (I did a lot of such googling when I was setting up bikes for the Ronde Van Calderdale which is famous for its 20% gradient climbs!).

Claris, Sora, Tiagra, 105 & Ultegra all have mechs rated to work with a 32t cassette these days and there are 8,9,10 & 11spd Shimano cassettes available with a 32t large sprocket that you will find specced on various road bikes.